You're pretty much contradicting yourself there. FPS is a measure of how many frames are changed per second, and you are saying that our eyes see change, so they should be able to see frames being changed.
No, changes
over time. Think analog signaling: there are rising and falling levels, not ons and offs.
If you actually move something slowly in front of you, you have a nice gradual change. You detect motion. The other sensors in your eyes can be used to confirm this and compliment it. If you could see it as images, they would be blurry. Your eyes' response is fairly slow, and the processing of all the information together in your brain is what creates what you perceive as a clear image of a thing moving.
Now, move that something very fast. You don't see motion. A very fast fan, for instance, simply looks translucent.
On the opposite side of things, if you take something from a stop to moving extremely fast to a stop, again, it will almost look like it instantly moved...but you will see a little bit of it over the course of the movement, usually, giving your brain enough hints. The faster this movement, the more perfectly-focused static images you would need to percieve motion (in the absence of added motion blur).
What you said makes no sense. The amount of movement that our eyes see can be measured in frames per second, as can any other amount of movement.
Er, no.
If and only if you record or render enough frames to saturate your ability to detect that these images are not being instantly swapped out (typically, with peripheral vision not accounted for, that's somewhere in the low 20s),
and those frames have enough motion blur to mimic what your eyes might otherwise see,
then there is enough information that you don't see that there are separate frames.
In games, the above is not true, due to the lack of motion blur, and that we are often close enough to the monitor to utilize peripheral vision. Every image is like a perfect photograph. Watch a high-profile sports event, or average new action movie, and you can see this, too: each frame looks great paused, but it is difficult to perceive motion. Then watch an old movie--old war movies are good for this, as they tend to have a lot of jarring movements--and you can see the opposite, with fuzzy still frames, but where you can perceive fine details and even read small print when the movie is playing. Recent animated CGI movies will tend to be on one side or the other of this. While you don't see each and every frame, you end up with a few frames effectively mashed on top of one another, but still without the information that your brain wants to be able to see that things are moving. It's a fitting analogy to say that you see the dots, but not lines connecting them.
As of yet, there have been very few attempts to create a game engine that is either real-time (vary rendered detail per frame to meet a known deadline, like maybe 15ms/frame), or that can predict how long the current and next frame will take to render (which need to be known for accurate motion blur with varying frame rates), one of which would be required to implement
good motion blur.
However, there is another way to get around that problem: render enough frames quickly enough that motion blur, like good films have, is not necessary.
Finally, there are natural differences among us, and also it is something that can be trained. Playing fast-paced games all the time, on systems that can put out high frame rates, can make you more sensitive to frame rate dips and input lag.
Also, 120Hz monitors can reduce perceived input lag, when actually rendering fewer frames, especially when combined with vsync.